A. Field of Invention
This invention relates to an improved method of grouting soil mediums. More specifically this invention is directed to the grouting of fined grained soil medium using a dilute suspension of cementatious particles in water.
B. Prior Art
Grouting has been used for more than a century to improve the engineering properties of soils. Grouts can be classified on the basis of their principle ingredients into two categories, suspension grouts and chemical grouts. Suspension grouts include cement and bentonite, whereas chemial grouts include sodium silicate, acrylate, and acrylamide. Suspension grouting has been traditionally limited to course sands and larger grained soil mediums. The range of soils that can be successfully grouted is limited by the grain size of the materials utilized to prepare the grout.
Chemical grouts are commonly prepared with organic monomers diluted with water. By adding a catalyst, such as an acid agent or a polyvalent salt, the aqueous solution of monomer is transformed into a gel that sets over a period of time to a solid mass. In general, the viscosity of chemical grouts is low and does not change before mass polymerization occurs. This allows chemical grouts to be injected into fine sands and/or silty soils. However, various components of chemical grouts, such as those used with acrylamide and polyurethane grouts, are highly toxic and are known to contaminate ground water.
With the drawbacks associated with chemical grouting and the limitations on the particle size of conventional suspension grouting materials there has been an effort to obtain suspension type grouts with the appropriate gradation of suspended solids to penetrate into fine sand formations and to develop guidelines for the use of such grouts in construction. To this end the use of microfine cement has been suggested. Microfine cement is a cementatious grouting material composed of ultrafine particles that may be used for stablizing all types of earth foundations. A water to microfine cement ratio of up to 3:1 has been recommended for grouting of fine grained sands.
The art is replete with a wide variety of materials and processes to stabilize soils, or improve subgrades in the subsurface layers adjacent to the surface of the earth for a variety of purposes. For example, U.S. Pat. No. 1,929,215 (Poulter) discloses a method of raising and backfilling pavement. The mixture employed comprises soil, cement and water, with a water to cement ratio of 12:1. This mixture is then pumped into void spaces under rigid type pavements to correct settlement or deficiencies in subgrades. High pumping pressure is required to achieve the hydrostatic power necessary to lift the pavement being raised. A means for solidifying underground structures using a grout that penetrates a great distance is disclosed in U.S. Pat. No. 2,233,872 (Procter). The grout composition is composed of cement, water and a gel. No setting of the grout nor a change in hardness of the soil, is observed when using a grout mixture having a water:cement ratio greater than 3.5. further, a pressure of 30 to 50 psi is required to inject grout mixtures of the Procter invention. Likewise, U.S. Pat. No. 4,540,316, (Takahashi) teaches an impregnation method which uses a mixture of cement, bentonite, water, and a naturally occurring waste material in the proportions of 1.0:1.0-3.5:0.5-2.0.
In summary, the art has recognized various grouting techniques, including the use of microfine cement for penetrating soil medium having fine grained particles. However, the art has not recognized the use of a dilute suspension type grouting method that operates at low a constant pressure and can penetrate fine grained soil mediums without causing soil fracture.